Ford F150 - Air conditioning on when air set to vent

My air conditioning is coming on when I set the air to panel or floor. I'm only getting about 10 mpg in the winter and 12 in the summer and trying to find ways to get a little better mileage. It doesn't do it all of the time but now with winter coming on, there is no way to tell how often it is happening.

Any idea what could be causing this?

when its on panel or floor, and you set the temp knob to hot does it get hot? or does it stay cold? how many miles on your truck?

it gets hot.

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